Visitors

To walk the whole graph of an already-parsed type, use the TypeLang\Parser\Traverser class. It accepts one or more TypeLang\Parser\Traverser\VisitorInterface implementations and calls each of them for every node it visits.

Let's write a visitor that prints the class name of every node it enters, using the convenience TypeLang\Parser\Traverser\Visitor abstract class (which no-ops every lifecycle method, so you only override what you need):

use TypeLang\Parser\Traverser;
use TypeLang\Parser\Traverser\Command;
use TypeLang\Parser\Traverser\Visitor;
use TypeLang\Type\Node;

$type = new TypeLang\Parser\TypeParser()
    ->parse('array<array-key, object{ key?: int<0, max> }>');

$visitor = new class extends Visitor {
    public function enter(Node $node): ?Command
    {
        echo \sprintf(" - %s\n", $node::class);

        return null;
    }
};

Traverser::new([$visitor])
    ->traverse([$type]);

- TypeLang\Type\NamedTypeNode - TypeLang\Type\Name - TypeLang\Type\Identifier - TypeLang\Type\Template\TemplateArgumentListNode - TypeLang\Type\Template\TemplateArgumentNode - TypeLang\Type\NamedTypeNode - TypeLang\Type\Name - TypeLang\Type\Identifier - TypeLang\Type\Template\TemplateArgumentNode - TypeLang\Type\NamedTypeNode - TypeLang\Type\Name - TypeLang\Type\Identifier - TypeLang\Type\Shape\FieldsListNode - TypeLang\Type\Shape\NamedFieldNode - TypeLang\Type\Identifier - TypeLang\Type\NamedTypeNode - TypeLang\Type\Name - TypeLang\Type\Identifier - TypeLang\Type\Template\TemplateArgumentListNode - TypeLang\Type\Template\TemplateArgumentNode - TypeLang\Type\Literal\IntLiteralNode - TypeLang\Type\Template\TemplateArgumentNode - TypeLang\Type\NamedTypeNode - TypeLang\Type\Name - TypeLang\Type\Identifier

The Visitor Lifecycle

VisitorInterface (and its Visitor no-op base class) has four methods, called in this order for a single traverse() call:

Method	Called
`before(): void`	once, before the first node is visited
`enter(Node $node): ?Command`	once per node, on the way down, before its children
`leave(Node $node): void`	once per node, on the way back up, after its children
`after(): void`	once, after the last node has been visited

before
enter UnionTypeNode
  enter NamedTypeNode(int)
  leave NamedTypeNode(int)
  enter NamedTypeNode(string)
  leave NamedTypeNode(string)
leave UnionTypeNode
after

enter() may return TypeLang\Parser\Traverser\Command::SkipChildren to prevent the traverser from descending into that node's children — leave() is still called for the node itself, just not for anything beneath it.

use TypeLang\Type\Template\TemplateArgumentNode;

$visitor =  new class extends Visitor {
    public function enter(Node $node): ?Command
    {
        if ($node instanceof TemplateArgumentNode) {
            return Command::SkipChildren;
        }

        echo \sprintf(" - %s\n", $node::class);

        return null;
    }
};

Traverser::new([$visitor])
    ->traverse([$type]);

Traverser API

new Traverser(iterable $visitors = []) — construct directly from a list of visitors, or use the equivalent static Traverser::new($visitors).
Traverser::through(VisitorInterface $visitor, iterable $nodes) — shortcut for the common "one visitor, traverse once, give it back to me" pattern — wraps the visitor in a new traverser, runs it, and returns the same visitor instance so you can immediately read state off it:
// Find & collect all "Name" nodes $find = Traverser::through(new ClassNameMatcherVisitor(Name::class), [ $type ]);
->with(VisitorInterface $visitor, bool $prepend = false) — returns a new traverser with an additional visitor appended (or prepended).
->withPropertyAccessor(PropertyAccessorInterface $propertyAccessor) — returns a new traverser that discovers a node's children through a custom PropertyAccessorInterface instead of the default reflection-based one — see below.

Custom Property Access

By default, the traverser discovers a node's children via Traverser\PropertyAccessor\SimplePropertyAccessor, which reflects over every non-static, non-hooked public and non-public property and descends into whichever ones hold a Node or an iterable of them. You can supply your own PropertyAccessorInterface implementation (e.g. to only look at a specific subset of properties, for performance or for a custom node hierarchy) via Traverser::withPropertyAccessor().

Built-in Visitors

MatcherVisitor / ClassNameMatcherVisitor: Find the first node matching an arbitrary predicate, or matching a given class. See MatcherVisitor and ClassNameMatcherVisitor.
DumperVisitor / StreamDumperVisitor / StringDumperVisitor: Render the whole tree as an indented, human-readable dump — to a stream or into a string. See DumperVisitor, StreamDumperVisitor, and StringDumperVisitor.
TypeMapVisitor: Rewrite every Name occurrence in a tree via a callback — the mechanism behind Name resolution. See TypeMapVisitor.

05 July 2026